This invention relates to compositions containing a polymercaptan and a compound which has both at least two allyl, methallyl, or 1-propenyl groups and at least one phenolic hydroxyl group. It also relates to the polymerisation of such compositions by means of actinic radiation or free-radical catalysts, to the further crosslinking, on heating, of polymerised products, alone or with a heat-curing agent, and to the use of such products as surface coatings, in printing plates, printed circuits, and reinforced composites, and as adhesives.
For a number of reasons it has become desirable to induce polymerisation of synthetic resin compositions by means of actinic radiation. Employing photopolymerisation procedures may, for example, avoid the use of organic solvents with their attendant risks of toxicity, flammability, and pollution, and the cost of recovering the solvent. Photopolymerisation enables insolubilisation of the resin composition to be restricted to define areas, i.e., those which have been irradiated, and so permits the production of printed circuits and printing plates or allows the bonding of substrates to be confined to requires zones. Further, in production processes, irradiation procedures are often more rapid than those involving heating and a consequential cooling process.
We have now found that valuable products can be made by photopolymerisation of compositions containing a polymercaptan and a compound which contains both at least one phenolic hydroxy group and at least two allyl, and/or methallyl, and/or 1-propenyl groups. We have found, too, that such compositions may also be polymerised by means of free-radical catalysts. The composition, comprising polymerised material containing residual phenolic hydroxyl groups, may be further crosslinked, i.e., converted into the insoluble, infusible, C-stage on heating by means of a heat-activated crosslinking agent for phenolaldehyde novolac resins contained therein. Hence, a stepwise cure is possible.